| 摘要 |
In a known method for radiographic imaging, a phosphor sheet capable of stimulation with radiation and carrying stored thereon an image pattern obtained e.g. by an X-ray exposure through a patient's body, is exposed to stimulating radiation, such as a laser beam, which causes the sheet to emit light in the pattern of the stored image and the emitted light is read-out photoelectrically. The stimulating radiation is applied to the sheet as a beam which is caused to scan the sheet linewise as the sheet undergoes relative movement in one direction with respect to the beam by means of galvanometric deflection which deflects the beam in one direction in a scanning step and then in the opposite direction in a retracing step to return the beam for the next scanning step. In the invention, the sheet is exposed to the beam at a significantly lower intensity level to cause the sheet to emit low level light corresponding to the image pattern. The low level light is read out as low level image signals which are then employed to control the sensitivity with which the light emitted as a result of the scanning step is read out photo-electrically, e.g. the gain utilized for such read-out. The opaque light chopper ordinarily employed to block the radiation beam during the retrace step is replaced with a chopper of limited light transmissivity, e.g. 5-10%, which reduces the intensity of the radiation beam during the retrace step so that the same light source can be used during both the scanning and retrace steps.
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